JPS6134192B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for preventing forgery of documents, and more particularly to a method and apparatus for preventing forgery of documents, which prevents forgery of documents such as paper defects, credit cards, and identification documents.

For example, paper, credit card, identification card, etc.
Most of the documents in use today, such as tickets, checks, etc., can be forged with some skill using modern reproduction methods. therefore recording an authentic mark on such document;
Preventing counterfeiting is too expensive, and therefore various methods have been proposed to increase security against counterfeiting. If the authenticity mark is made into a spatial structure and a mark that bends incident light in a predetermined direction is recorded on the document, the degree of prevention against forgery can be relatively improved. The production of such spatial structures, such as hologram-based structures, phase gratings and kinoforms, requires fairly expensive equipment. It is possible to verify the authenticity of such documents using automatic inspection equipment by measuring the spatial intensity distribution of the scattered light emanating from the spatial texture.

For example, German Patent No. 2,538,875 discloses a method in which a phase diffraction grating is recorded on a document, and the diffraction grating deflects light from a light source into diffracted rays of each order in a predetermined relationship. When the energy components of the diffracted rays of a predetermined order have a certain relationship with each other, it is determined that the document is genuine.

Furthermore, German Patent No. 2814890 describes a method for testing the authenticity of a phase grating recorded on a document by comparing the intensity of a light beam split into diffraction orders of a predetermined order with the intensity of diffusely scattered light. .

It is also known to embed an anti-counterfeiting line in the form of a flat metal or plastic strip with a rectangular cross section in the paper backing. This anti-counterfeiting line is easily visible and detectable, making it easy and quick to check the authenticity of the document.
At the same time, embedding such an anti-counterfeit line into a layer of paper or plastic requires considerable skill and requires a process that cannot be easily imitated. In order to further improve the anti-counterfeiting property and to mechanically check the existence of the anti-counterfeiting line and its authenticity, for example, German Patent No. 2205428 discloses that the anti-counterfeiting line is intentionally made with small holes representing a code pattern. A method is described in which the information is read out using a light beam or a particle beam.

Therefore, the present invention was devised in view of these points, and it is possible to reliably prevent genuine documents from being forged, and to record genuine information and easily read genuine information from this document. The purpose of this invention is to provide a method and device for preventing document forgery.

For example, in the present invention, "International U.S. Commission on Electromagnetic Waves"
RSI, Symposium 1980, Miyunchen 1980 8
A partially coherent light source with a periodic phase cross-section obtained by superimposing a phase grating and a scattering element as described in 2011, pp. 315C/1 to 315C/2. It is based on the recognition that in some cases the presence of periodic objects can be detected better by the degree of coherence than by the intensity.

The details of the present invention will be explained below based on embodiments shown in the drawings.

In FIG. 1, the reference numeral 1 refers to a document such as a piece of paper, a credit card, an identification card, a ticket, a check, etc., and this document 1 is a spatial organization having an optical element 2' having a determining element. It has one or more marks of authenticity as shown in structure 2.
Such a spatial organizational structure deflects transmitted light or reflected light in at least a predetermined direction by diffraction, and is, for example, a phase hologram, a phase diffraction grating, or a kinoform, and its authenticity depends on the spatial organizational structure2. The light scattered by can be inspected by using automatic inspection equipment. In the illustrated example, the optical element 2' with the determining element
consists of a phase grating imprinted on a thermoplastic substrate 3 and covered with a thin reflective layer 4. The protective layer 5 has a rough, diffusive scattering surface in the illustrated example and is intended to protect the phase grating as well as the reflective layer 4 from mechanical damage. The rough surface of the protective layer 5 forms a scattering element 2' which has a stochastic element and is diffused and scattered, and this is overlapped with an optical element 2' having a determining element to form a spatial structure. The substrate 3 on which the structure 2 is formed is preferably opaque and has a protective layer 5
Since it is transparent only to infrared rays, the optical element 2' having the determining element is at least invisible to the human eye.

Typical dimensions of the optical element 2′ with determining elements,
For example, in the case of a phase grating, the grating constant is illustrated in FIG. 1 by g, and the stochastic scattering element 2' correlation length is illustrated by g. Simply expressed, the correlation length is the average granularity of the surface roughness of the scattering element 2' having a stochastic element. More precisely, the probabilistic height growth h as a function of the length growth s
(s) still has some kind of correlation, ie h(s) is such a length that is still statistically correlated with h(s±n). Here, h is the height extension of the scattering element 2' having a stochastic element, and s is its length extension.

The protective layer 5 can be made of a material with a spatially varying refractive index, for example, and can have a flat surface. In this case, the correlation length n of the scattering element with stochastic elements is understood roughly as the average "granularity" of the variations in the refractive index.

The document 1' shown in FIG. 2 differs from the document 1 of FIG.

In Figure 3, the light ray 7 emitted from the light source 6 is the document 1.
(or 1'). The light beam 7 is at least quasi-monochromatic light and has a predetermined spatial coherence. That is, the coherence length immediately before the tissue structure 2 is at least as large as the representative dimension g of the optical element 2' having the determining element, and the diameter of the light beam is equal to the representative dimension g.
Must be bigger.

The light scattered by the tissue structure 2 is incident on two optical separation elements 8, 9, where it is preferably divided into narrow beams 10, 1 with variable scattering angles θ, θ'.
Only 1' is taken out. For example, a variable aperture, a mirror, or a prism is used as the optical selection elements 8 and 9. These elements 8, 9 are preferably placed synchronously, so that θ'=-θ always holds.

The light beam 10 passes through a deflection element 12 and an optical path difference forming element 13
Via the deflection element 14, the light beam 11 also enters a superimposition element 17 via the deflection elements 15, 16, where the light beams 10, 11 are combined again. The optical path difference forming element 13 changes the optical path difference δ between the light beams 10 and 11. Deflection element 12,1
4, 15, and 16 are, for example, mirrors, prisms, optical fibers, photoelectric deflectors, etc.; the optical path difference forming element 13 is, for example, a prism, a movable mirror, or a material having a variable refractive index; and a superposition element 17 are semi-transparent mirrors, optical fibers, etc.

The combined light beams 10 and 11 are sent to an optical sensor 1, which is composed of, for example, a photodiode or a photomultiplier tube.
Guided by 8. The optical sensor 18 is the signal processing circuit 1
9, and an electronic determination circuit 20 is connected to the downstream thereof.

A control device (not shown) controls the authenticity detection. In that case, each element 6, 8, 9, 13,
Mechanical or electrical control signals, start signals, and stop signals are sent to 18, 19, and 20, respectively.
The control device can also control a drive device (not shown), by means of which the document 1 is translated in order to form an average value of the values obtained by the measurements described below.

Before explaining the operation, the spatial organization structure of the document 2
is a symmetrical diffraction grating, and optical selection elements 8, 9
shall be adjusted so that θ=θ ₁ and θ′=θ−1=−θ ₁ . However, _θ1 is the angle of the first-order diffracted light, and θ- ₁ is the -1st angle of the diffraction grating.
Indicates the angle of the next diffracted light. The light source 6 is activated by the control device, and a light beam 10,
11, interference fringes are generated. The optical path difference forming element 13 is controlled by the control device so that the optical path difference δ changes continuously. As a result, as is clear from FIG. 4, the intensity I=I(δ) of the interference fringes varies between a maximum value I _nax and a minimum value I _nio . The optical sensor 18 detects the intensity I=I(δ), and the signal processing circuit 19 measures I _nax and I _nio , and based on the values, lμl=(I _nax − I _nio )/(I _nax + I _nio ). The so-called contrast l of the interference fringes according to the relationship
Calculate μl. The measured value of the contrast lμl is a value related to the degree of coherence of both the light beams 10 and 11, and is sent to the determination circuit 20 to form a determination signal of affirmation (yes) or negation (no).
For example, when the measured value of the contrast lμl exceeds a predetermined threshold, the determination circuit 20 considers the document 1 to be genuine and generates an affirmative signal.

In general, the contrast is a function of the scattering angles θ, θ′, ie, lμl=lμl=(θ,θ′)l. It is therefore preferable to vary the angles .theta., .theta.' by means of the drive, measure the contrast l.mu.l as a function of the angles .theta., .theta.', and compare the measured value in the decision circuit 20 with a stored threshold function. In this way, for example, a document on which a phase grating is formed can be identified as genuine only if the degree of coherence in the multiple orders of diffracted light is within a respective predetermined limit value.

FIG. 5 shows the angular intensity <I(θ)> of scattered light measured by a conventional intensity measurement method in various spatial structures. However, <...> indicates an average value. On the other hand, the contrast lμ(θ, -θ)l obtained by measuring the degree of coherence according to the present invention is illustrated in FIG. Note that in Figures 5a and 6a, the lattice constant is g.
5b and 6.
Figure b shows a pure diffuse scattering element with a correlation length of 〓g, and Figures 5c and 6c show the case where a phase diffraction grating is superimposed with a diffuse scattering element whose correlation length is 〓g.
Furthermore, Figures 5d and 6d show an example in which a phase diffraction grating is stacked on a diffuse scattering element with 〓g/10, and Figures 5e and 6e show an example in which a diffuse scattering element with 〓g/20 and a phase diffraction grating are overlapped. Examples of stacked diffraction gratings are shown below.

In the coherence measuring method according to the present invention, even when the authenticity mark is strongly disturbed by scattering elements with stochastic elements and it is difficult and sometimes impossible to measure the authenticity by intensity distribution,
It can be seen that reliable authenticity judgments can be made. Coherence measurement methods therefore make it possible to identify authenticity marks, which are formed, for example, by phase gratings, holograms, etc., which are placed on rough substrates or which are disturbed by, for example, attraction. Security against counterfeiting is based on organizational structure 2
The optical element 2'' having determining elements is shown in FIGS. 1 and 2.
As shown in the figure, it can be further raised when superimposed with a scattering element 2'' having a stochastic element that intentionally causes diffuse scattering.Both elements 2',
2", it becomes difficult or impossible to identify the authenticity mark by strength measurement, but
Authenticity can be determined by measuring the degree of coherence. In particular, if the correlation length of the scattering element 2' having a stochastic element is at most about 1/5 of the dimension g of the optical element 2' having a determining element, it can be reliably identified.

FIG. 7 shows a simplified apparatus for measuring the degree of coherence using interferometry. In this figure, the same parts as those shown in FIG. 3 are given the same reference numerals. Luminous flux 1
0 and 11 are taken out by two mirrors 21 and 22, and further directed to a common detection plane 25 by two mirrors 23 and 24. The angles θ and θ' are adjusted to θ=θ ₁ and θ′=−θ ₁ . The document 1 is held by a swingable holding device, not shown, so that the angle between the surface of the document 1 and the perpendicular to the axis of the light beam 7 can be varied. Optical sensors 26 and 27 connected to the signal processing circuit 19 are arranged on the detection surface 25, one optical sensor detects the bright part of the interference fringes, while the other optical sensor detects the dark part. The signal processing circuit 19 detects the difference in intensity measured by the optical sensors 26 and 27, for example.

The angle is varied, in which case = 0 corresponds to normal incidence of the ray 7, and as is clear from FIGS. The contrast is lμl. For this, if is not 0, the 9th
No contrast appears as shown in the figure.
The determination circuit 20 generates an affirmative (yes) signal when the contrast lμl becomes greater than a predetermined threshold. Further, when the positive signal is generated only when the change when the document 1 is swung exceeds a predetermined value, the reliability of the authenticity determination can be increased.

Instead of the contrast lμl of the interference fringes, it is also possible to measure the so-called second-order intensity correlation g ² . This will be explained with reference to FIGS. 11 and 12. The parts 6, 8, 9, 12, 15 of the device shown in FIG. 11 each correspond to those in FIG. The light beams 10 and 11 deflected by the deflection elements 12 and 15 enter optical sensors 28 and 29. Both optical sensors 28 and 29 are connected to a signal processing circuit 30
(e.g. equipped with an electronic correlator),
A determination circuit 31 is connected to the subsequent stage.

When determining the authenticity of document 1, the angles θ, θ′
is changed continuously. The signal processing circuit 30 functions as an electronic correlator, and g ² (θ, θ′)=<I(θ)・I(θ)>/<I(θ
)>・<I(θ)> The intensity correlation g ² (θ, θ′) is measured according to the formula.

When the cross section of the light beams 10 and 11 is sufficiently large, l
The quantities μl and g ² follow the well-known relationship g ² = 1 + lμ
connected by l ² . An affirmative signal appears at the output of the determination circuit 31 when the intensity correlation g ² exceeds a predetermined threshold.

FIG. 12 shows a simplified device for measuring intensity correlations. Optical sensor 28,2
9 functions as an optical selection element and a detector at the same time. The angle θ is fixed to the value of the first order diffracted light, where θ=θ ₁ . Since the optical sensor 29 is movable, the angle θ' can be changed by Δθ, such that θ'=−θ ₁ ±Δθ. The intensity correlation g ² is maximum when Δθ=0.

In the apparatus illustrated in FIGS. 11 and 12, a single optical sensor can be used instead of optical sensors 28, 29. In this case, for example, first the function I(θ) is measured, the measured value is stored analogue or digitally, and then the function I(θ) is
(θ′) is detected and g ² is calculated. This can be done in a relatively simple way by using a photomultiplier tube as the light sensor and an electronic counter as the memory. Such correlation measurements are, for example, {Photon Correlation and Light
Beating Spectroscopy” 1974, Plenum Press,
Since it is described in the New York book, I will not discuss it in detail here.

Next, referring to FIGS. 13 to 19, it is more compatible with ordinary document preparation methods than embedding fine tissue structures that diffract light, and moreover, safety against forgery is guaranteed, in which case the authenticity mark We will explain how to make it invisible to the human eye. In FIG. 13, reference numeral 41 indicates documents, such as paper, credit cards, identification cards, train tickets, and checks. The substrate 42 of the document 41 is made of plastic, paper or cardboard, for example. The substrate 42 includes an optical element 43' having macroscopic determining elements and a scattering element 4.
An authenticity mark is recorded consisting of a spatial organization structure 43 consisting of 3". Macroscopic optical element 43'
has spatial coherence and is configured to deflect a light ray 44 incident on the document 41 into at least two predetermined directions 45 and 46 by refraction or reflection (refraction in this embodiment) according to the laws of geometric optics. be done. A light ray 44 is diffusely scattered by a scattering element 43'' having a stochastic element that is functionally superimposed on this macroscopic optical element 43', and based on the intensity distribution 47 of the scattered light, the macroscopic optical element 4
3' becomes difficult or even impossible to distinguish, and in that case the scattered light is mutually coherent in the predetermined directions 45, 46.
is configured to be. The scattering element 43'' is formed by the surface structure or material of the substrate 42 or the optical element 43'.

The scattering angle of any ray portion 48 of the light scattered by the tissue structure 43 is illustrated in FIG. θ, and the scattering angle of the light beam portion scattered in the predetermined directions 45 and 46 is θ.
_s and −θ _s , respectively.

When testing the authenticity of a document 41 by an automatic testing device, a light beam 44 is generated from a light source and projected onto a tissue structure 43 . The light scattered by the tissue structure 43 is extracted as a narrow beam in predetermined directions 45 and 46, respectively. A quantity that is related to the degree of mutual coherence is measured from both light beams using at least one light sensor and an electronic signal processing circuit.
An affirmative signal or a negative signal is detected from this measured quantity using a decision circuit. In this case, the document 41 is judged to be genuine when the degree of coherence, ie, the contrast lμl or the intensity correlation ^g2 , exceeds a predetermined threshold. In order to measure the degree of coherence, Figures 3, 7, 11 and 1
The apparatus illustrated in Figure 2 is used.

FIG. 14 shows the relationship between the contrast lμl and the angle Δθ. From the same figure, △θ=2
It can be seen that it has a maximum value when θ _s . Therefore, by measuring the degree of coherence based on this maximum value, the presence of an optical element 43' having a macroscopic determining element in the document 41 is detected. Since the incident light is diffused and scattered by the scattering element 43'' of the tissue structure 43, the authenticity mark of the tissue structure 43 becomes invisible to the human eye.

The distribution of light scattered by the texture structure 43 usually has a granular nature, which makes it difficult to measure the degree of coherence if the granularity is static. However, when measuring the degree of coherence, this drawback can be overcome by, for example, continuously moving the document 41 and finding the average value of the light patterns generated at that time. Preferably, document 41 is moved parallel to the longitudinal axis of optical element 43'.

As the macroscopic optical element 43', for example, a means for dividing light such as a double prism, a half mirror, a reflector having an appropriate inclined surface, etc. is embedded in a material that diffuses and scatters or a material that has a surface structure that diffuses and scatters. It is preferable to use such an optical means. Next, these will be explained in detail with reference to FIGS. 15 to 19.

FIG. 15 shows a document 50 in which a strip 51 is embedded in a substrate 42. The upper and lower surfaces of this strip 51 are composed of two surfaces 52 and 53 that are inclined at a gentle angle to each other. The width of the strip 51 is approximately 1 mm, and the length is approximately 1 mm.
corresponds to the length or width of The strip 51 is preferably made of metal, metal-coated material or transparent material. Substrate 42 may be comprised of, for example, diffusing paper or a thermoplastic material with a diffusing and scattering surface.

FIG. 16 shows a document 54 having a reflective surface and a strip 55 embedded in the substrate 42. The strip 55 has an approximately rectangular cross-section and is bent slightly obliquely to its longitudinal centerline, so that slightly oblique surfaces 52, 53 appear.

The substrate of the document 56 illustrated in FIG. 17 consists of two layers 5 of transparent plastic bonded together.
It consists of 7,58. The outer surfaces of layers 57 and 58 have no texture and are smooth;
The boundary surface 59 of 58 is processed so as to cause dispersion and scattering. This surface functions as a beam splitter and splits the obliquely incident beam 60 into a reflection direction 61 and a transmission direction 62. The rough interface 59 also functions as a scattering element that diffuses and scatters the light rays 60. When determining authenticity,
The light scattered by the document 56 is reflected light 61 and transmitted light 6
The light beam is separated into two narrow beams, and the degree of coherence thereof is measured.

Further, FIG. 18 shows a document 63 equipped with a board 42.
is shown, with a transparent strip 6 on its substrate.
4 is embedded. The cross section of the strip is rectangular, and one surface thereof is coated with a thin translucent reflective layer 65. This reflective layer 65 splits the light beam and forms a macroscopic optical element. A scattering element is formed by giving the material or surface structure of the substrate 42 a property of diffusing and scattering. The authenticity check is performed in the same way as for document 56.

FIG. 19 shows a plurality of inclined surfaces 68 on the substrate 42.
Illustrated is a document 66 with an embedded block 67. These surfaces 68 divide the incident light into a plurality of beam portions by reflection or refraction, and the substrate 42 causes the incident light to be diffusely scattered.
Therefore, in this case, the scattered light becomes mutually coherent in a plurality of predetermined directions. Preferably, the code pattern is arranged in these directions. When testing authenticity, a plurality of narrow beams are taken out and the code pattern is read out by measuring the degree of coherence.

20 and 21 illustrate a document 71 having a spatial structure 72 as illustrated in FIGS. 1, 2, and 15-19. This tissue structure is illuminated by a light source 73 that is at least quasi-monochromatic and spatially coherent.
Two narrow beams of light scattered by the tissue structure 72 are incident on the optical selection means 74, 75, 74', 75'. These means are provided with deflection elements, means for changing the optical path difference, and the like. The average scattering angles of both scattered light beams are indicated by θ ₁ and θ ₂ . A superimposing element 76 superimposes the two separated beams again. The superimposed beams are received by a detection device 77, which generates electrical signals, which are then processed to make a positive or negative decision, and the results are recorded. Various optical means 73-77 are fixedly or movably mounted on a base (not shown).

The apparatus illustrated in FIGS. 20 and 21 is characterized by image inversion (e.g. reflection) in which both light beams encounter optical separation elements 74, 75, 74', 75' and from tissue structure 72 before being superimposed again in superposition element 76. The number of times is different. In the device shown in FIG. 20, the number of image inversions is an odd number, and in the device shown in FIG. 21, it is an even number.

The method of superimposing the separated light beams is determined by the number of inversions. If the number of times is odd, the superposition is reversed, and if it is even, it is normal. Inverse superposition corresponds to detecting coherence symmetrically, and normal superposition corresponds to detecting coherence asymmetrically.

If the light beam is even slightly deviated from the average scattering direction due to the geometrical characteristics of the device as described above, the received light beam will be correspondingly deviated as well. Conversely, the declination angle Δθ in the detection device 77 corresponds to the declination angles Δθ ₁ and Δθ ₂ of the separated light beams.
In the case of reverse superposition, the declination angles △θ ₁ and △θ ₂ have various signs (the 20th
figure). In addition, in the case of normal superposition, the declination angle △
The signs of θ ₁ and △θ ₂ are always the same (21st
figure).

To summarize here, Fig. 20 is an inverse superposition, the number of inversions is odd and corresponds to symmetry detection, and △
The signs of θ ₁ and Δθ ₂ are different.

On the other hand, in the case of normal superposition (Fig. 21), the number of inversions is an even number, which corresponds to asymmetric detection, and △θ
₁ and △θ ₂ have the same sign.

The contrast lμl of the interference fringes appearing on the detection surface of the detection device 77 is related to the average scattering angles θ ₁ , θ ₂ and the deviation angle Δθ. FIGS. 22 and 23 show the function lμl=(θ ₁ , θ
The average values of ₂ ) are shown schematically. FIGS. 24 and 25 illustrate the relationship between the contrast lμl and the deviation angle Δθ when the average scattering angles θ ₁ and θ ₂ are fixed.

The curve illustrated at 78 in FIGS. 22 and 24 corresponds to a symmetrical detection having a series of discrete maxima.

In the case of asymmetric detection, curves 79 and 80 are generated which provide a constant contrast over a fairly wide angular range, as shown in FIGS. 23 and 25. The maximum values of the curves 79 and 80 change depending on where the main direction is chosen, that is, the scattering angles θ ₁ and θ ₂ . If sinθ ₁ - sinθ ₂ takes “appropriate” values, the argument △θ
large contrast lμl over a wide range of
occurs. On the other hand, if sin θ ₁ -sin θ ₂ differs even slightly from this value, substantially no contrast will occur as shown in curve 80.

The "appropriate" values of sin θ ₁ -sin θ ₂ are determined by the diffraction or scattering properties of the texture 72 of the authenticity mark. Such values are determined by each pair of scattering directions in which the tissue structure 72 concentrates the intensity of the scattered light. For example, in the case of periodic gratings such suitable values are always integer multiples of λ/b. However, λ is the wavelength of the light source 73,
b is the grating period.

From the above, in the case of normal overlay, the following measurement method can be obtained. First, the main directions are adjusted to appropriate values θ ₁ and θ ₂ . Generally, these directions are not limited to a predetermined plane, but
For simplicity, angles θ ₁ and θ ₂ are shown in this case. If the principal direction is chosen so that the difference between sin θ ₁ and sin θ ₂ is matched to the characteristics of the authenticity mark, a clear interference fringe of a predetermined width will appear on the detection surface, and its intensity distribution will be represented by curve 81 in Fig. 27. It has the shape shown and can be easily detected. but
If the difference between sin θ ₁ and sin θ ₂ is incorrectly selected, or if there is no authenticity mark on the document 71 in the first place, there is simply a diffused mark on the detection surface, as shown by curve 82 in Figure 27. Only the intensity distribution appears.

On the other hand, in the case of reverse overlapping, relatively narrow interference fringes appear on the detection surface, as is clear from FIG. 26, compared to the case of normal overlapping.

Particularly in the case of normal superposition, the above-mentioned change in intensity, that is, the presence of interference fringes on the detection surface, is a desirable quantity for forming a positive signal or a negative signal. Similarly, changes in intensity serve as a measure for measuring the degree of coherence, and can be detected as the original degree of coherence using simple measurement techniques. In the apparatus of FIG. 28, the same parts as in FIG. 21 are given the same reference numerals.
In the same figure, the change in intensity can be detected on the detection surface using a single optical sensor 83, in which case the position of the optical sensor 83 is set at the angle of deviation Δθ shown in FIG.
can be varied by an amount of ±x corresponding to .
Although not shown in FIG. 28, the change in intensity is compared with a stored threshold value or threshold function using a signal processing circuit, and an affirmative or negative determination is made. Instead of moving the optical sensors, it is also possible to fix a group of optical sensors.

FIG. 29 shows an example of a simple device for detecting symmetry. The document 71 to be inspected is arranged on one leg of an angled holding member 84, and a mirror 85 is arranged on the other leg. The light source 73 and the holding member 84 provided with the document 71 and the mirror 85 are fixed on a table (not shown) that can swing around an axis 86 . Furthermore, two optical sorting elements 87, 88 and a detection device 89 are fixedly arranged. The detection device 89 may be, for example, a device for measuring correlation as shown in FIG. 3, or a measuring device using interference as shown in FIG.

In Figure 29, the angle formed by the legs of the stand is
Further, the angle between the surface of the document 71 and the surface of the mirror 85 is represented by α, and the angle between the surface of the document 71 and the direction of incidence of the light beam is represented by β. The angle formed between the light beam directly incident on the optical selection element 87 and the light beam reflected by the mirror 85 and incident on the optical selection means 88 is shown.
Also, the average scattering angle of both separated beams is θ
₁ , _θ2 .

For such a geometrical configuration, the separated scattering angles θ ₁ , θ ₂ are θ ₁ =c+ and θ ₂ =
given by c′−. However, c and c' are constants. By swinging the table by an angle, the angles θ ₁ and θ ₂ are changed in opposite directions. Angle θ ₁ ,
For the sum of θ ₂ , the following formula holds true: θ ₁ +θ ₂ =γ+2(α+β−π). The angles α, β, and γ are 0 on the right side of the equation.
When selected so that θ ₁ =−θ ₂ holds true. In other words, this is symmetrical detection in a narrow sense. Only a single mechanical movement is required for this purpose.

If we choose θ ₂ =θ ₁ in FIG. 20, symmetrical detection can be obtained by changing the wavelength of the light source 73.

FIG. 30 shows a document 90, in which a spatial organization structure 91 is arranged on a substrate 92 arranged diagonally throughout the document. The effective surface of the tissue 91, which preferably has a microscopic structure, is thereby hidden and the security against counterfeiting is increased. Texture structure 91 can be better concealed when document 90 is composed of a diffusely scattering material forming stochastic scattering elements. Tissue structure 91 is preferably disposed obliquely on substrate 92 as illustrated in FIG. When such substrates 92 having various orientations are included in the document 90, the overall structure is such that their scattering or diffraction directions do not all lie in one plane.

The document 93 illustrated in FIG. 32 is comprised of an embedded substrate 94 with macroscopic sawtooth structures 95 and microscopic structures 96 superimposed thereon.
Refraction or reflection is performed by the macroscopic structure 95 according to the laws of geometric optics, and the microscopic structure 9
6 causes a certain diffraction so that the scattering or diffraction directions are not all in the same plane.

A substrate 98 is embedded in the document 97 illustrated in FIG.
9 and is coated with an anti-transparent reflective layer 100. The reflective layer 100 serves as a light beam splitter and separates obliquely incident light beams into light beams in a reflection direction and a transmission direction. A diffractive structure 99 splits the light beam further away into another plane. When the determining scattering element formed by the reflective layer 100 and the diffractive structure 99 is superimposed with a scattering element having a stochastic element, the diffractive structure 9 can be easily
9 can be made intentionally not geometrically clean.

FIG. 34 shows a counterfeit prevention line 101 embedded in a document as an authenticity mark. The macroscopic cross section of this anti-counterfeit wire 101 has a certain shape different from rectangular or circular over at least a predetermined partial length, while its surface has a microscopic uneven structure 102. The combination of this macroscopic cross-section and the microscopic relief structure 102 forms an authenticity mark that cannot be imitated by simple methods, resulting in a large number of characteristic scattering directions.

As explained above, according to the present invention, an optical element having a spatial organization structure determining element indicating an authenticity mark is formed by superimposing a diffuse scattering element having a stochastic element, and the intensity is determined by the scattering element. Since it is made difficult to identify an authentic mark by measurement and a quantity related to the degree of coherence is measured, it is possible to reliably determine the authenticity of the mark.

[Brief explanation of the drawing]

Each figure shows an embodiment according to the present invention, and FIGS. 1 and 2 are cross-sectional views showing a cross section of a document according to a different embodiment, and FIG. 3 is a configuration of an apparatus for inspecting the authenticity of a document. FIG. 4 is a diagram showing the characteristics of the intensity distribution obtained with the apparatus of FIG. 3, FIGS. 5a to 5e are diagrams showing the characteristics of various intensity distributions, and FIG. Figures 6-6e are diagrams showing the degree of coherence of different embodiments, Figure 7 is a block diagram showing another embodiment for testing authenticity, and Figures 8 and 9 are intensity distributions. FIG. 10 is a diagram illustrating coherence characteristics; FIGS. 11 and 12 are block diagrams illustrating configurations of different embodiments of the authenticity testing device according to the present invention; FIG. The figure is an explanatory diagram explaining another embodiment for testing authenticity, Figure 14 is a diagram showing characteristics of the degree of coherence, and Figures 15 to 1.
9 is a sectional view showing various embodiments of documents to be inspected according to the present invention, FIGS. 20 and 21 are block diagrams showing the configuration of other embodiments of the apparatus according to the present invention, and FIG. 24 and 25 are graphs showing the characteristics of the degree of coherence, and FIGS. 26 and 27 are graphs showing the output results of the computer calculation of the degree of coherence. A diagram showing the distribution, FIGS. 28 and 29 are block diagrams showing the configuration of other embodiments of the apparatus of the present invention, and FIG. 30 is a sectional view showing the internal configuration of the document used in the present invention. , FIG. 31 is a perspective view of the substrate used in FIG. 30, FIGS. 32 and 33 are cross-sectional views showing other configurations of documents used in the present invention, and FIG. 34 is a diagram of an element for preventing forgery. FIG. 2 is a perspective view showing an overview. DESCRIPTION OF SYMBOLS 1...Document, 2...Spatial organization structure, 2'...Optical element having a determining element, 3...Substrate, 4...Reflection layer, 5...
Protective layer, 2'... Diffusion scattering element, 8, 9... Optical sorting element, 13... Optical path difference forming element, 17... Superposition element, 19... Signal processing circuit, 20... Judgment circuit,
25... Detection surface, 26, 27... Optical sensor, 28, 2
9... Optical sensor, 30... Signal processing circuit, 31... Judgment circuit, 41... Document, 42... Substrate, 43'... Optical element, 43''... Scattering element.

Claims (1)

Claims: 1. At least one authenticity mark is recorded on the document in the form of a spatial tissue structure, said tissue structure is illuminated by a light source in an automatic inspection device, and at least two of the light scattered by the tissue structure are detected. A narrow beam of light is extracted and a quantity characterizing the tissue structure is detected from said beams using at least one light sensor and an electronic signal processing circuit, from which a positive or negative signal is formed using a decision circuit. In the document counterfeiting prevention method for inspecting the authenticity of the type and preventing document counterfeiting, the spatial organization structure 2 forms an amount (1 μl; g ² ) between both light beams that is related to the degree of coherence. Further, the spatial organization structure is formed by superimposing an optical element 2' having a determining element and a diffuse scattering element 2'' having a probabilistic element, and the authenticity mark is determined by intensity measurement by the scattering element 2''. A method for preventing forgery of documents, comprising: making identification difficult, and forming an affirmative signal or a negative signal by measuring a quantity related to the degree of coherence formed between the two light beams. 2. The two light beams are superimposed on each other, in which case the contrast (lμl) of the interference fringes that occurs is measured and is used as a measuring variable for forming a positive or negative signal.
Methods for preventing forgery of documents as described in Section. 3. The method for preventing forgery of documents according to claim 1, wherein the intensity correlation (g ² ) of the two luminous fluxes is measured and used as a measurement quantity for forming a positive or negative signal. 4. Preventing document forgery according to claim 1, wherein both the light beams are superimposed on each other and directed onto a detection surface, and the change in light intensity is used as a measurement quantity to form an affirmative or negative signal. Method. 5. The document according to claim 1, wherein the correlation length () of the scattering element 2'' is selected to be at most 1/5 of the typical dimension (g) of the optical element 2' having the determining element. 6. The spatial organization structure 43 is formed from macroscopic optical elements 43, 51, 55, 59, 65, 67 and scattering elements 43'', in which case the spatial organization structure 4
According to the laws of geometrical optics, the light 44, 60 incident on the optical element 3 is directed by the optical element into at least two predetermined directions 45, 46, 61,
Furthermore, the scattering element 43'' makes it difficult to detect the macroscopic optical element based on the intensity pattern 47 of the scattered light, and the scattered light is directed in the predetermined directions 45, 46, 61, 62. The method for preventing forgery of a document according to any one of claims 1, 2, 3, or 5, in which the document is diffusely scattered so as to be mutually coherent. 7. The spatial organization structure 91 The method for preventing forgery of a document according to claim 1 or 6, wherein the substrate 92 is arranged on a substrate 92, and the substrate 92 is embedded in the document 90. 8. The spatial organization structure is a macroscopic structure 95, 100.
and the microscopic structures 96 and 99, the method for preventing forgery of documents according to claim 1 or 6. 9. The document forgery prevention method according to claim 1 or 6, wherein a translucent reflective layer 100 is superimposed on the spatial organization structure 99. 10 An anti-counterfeiting line 101 is embedded in the document, and its macroscopic cross section has a certain shape different from a rectangle or a circle over a predetermined length, and its surface has a microscopic uneven structure 102. A method for preventing forgery of documents according to claim 1 or 6. 11. The document forgery prevention method according to claim 7, wherein the tissue structure 91 is arranged obliquely on the substrate 92. 12 A strip 5 as the macroscopic optical element 43'
1, 55 is embedded in the substrate 42, in which case at least one surface is comprised of at least two surfaces 52, 53 that are inclined to each other. 13. The document forgery prevention method according to claim 12, wherein the strip 55 has a rectangular cross section, is bent along one line, and is embedded in the substrate 42. 14. The document forgery prevention method according to claim 6, wherein light beam splitters 59, 65 are embedded in the substrates 42, 57, 58 as the macroscopic optical element 43'. 15 The beam splitter 59 separates the two layers 5 of the substrate.
15. The method for preventing forgery of a document according to claim 14, which is constituted by a boundary surface having irregularities of 7 and 58. 16 Translucent reflective layer 65 as beam splitter 65
is arranged on a transparent strip 64, which is connected to the substrate 42.
A method for preventing forgery of documents as set forth in claim 14 embedded in . 17. The document forgery prevention method according to claim 6, wherein a block 67 having a plurality of inclined surfaces 68 is embedded in the substrate 42 as the macroscopic optical element 43'. 18. The document forgery prevention method according to any one of claims 6 and 12 to 17, wherein the scattering element 43'' is formed by the material or surface structure of the substrate 42. 19. The scattering element 43″ is a macroscopic optical element 4
Any one of claims 6 and 12 to 17 formed by the material or surface structure of 3', 51, 55, 59, 65, and 67.
Methods for preventing forgery of documents as described in section. 20. The document forgery prevention method according to claim 12 or 17, wherein the macroscopic optical elements 51 and 67 are made of a transparent material. 21 The macroscopic optical elements 51, 55, and 67 are made of metal or a material coated with metal in claim 12, 13, or 17.
Methods for preventing forgery of documents as described in section. 22. The method for preventing forgery of a document according to any one of claims 6 and 12 to 21, wherein at least one code pattern is arranged in a predetermined direction in which the scattered light is mutually coherent. . 23 Claim 4, wherein the optical sensor 83 detects the presence or absence of interference fringes on the detection surface.
Methods for preventing forgery of documents as described in section. 24. An inspection device is provided for testing the authenticity of a document recording at least one authenticity mark in the form of a spatial tissue structure, the inspection device comprising a light source 6 illuminating said tissue structure 2, 43 and a light source 6 scattering by said tissue structure. at least two optical selection elements 8, 9 each extracting a narrow beam of light from the emitted light; at least one optical sensor; and an electronic signal processing circuit 19, 30 for detecting quantities characterizing said tissue structure.
and a determination circuit 2 that forms an affirmative or negative signal.
0, 31, said tissue structure 2, 43 has an optical element 2', 43' with a determining element and a diffuse scattering element 2'', 43'' with a stochastic element, in which case said scattering element 2 The correlation length () of ``, 43'' is at most 1/5 of the typical dimension (g) of the optical element having the determining element, and the signal processing circuit 19, 3
0 is a document forgery prevention device characterized in that it is configured to generate a measured quantity related to the degree of coherence of both light beams. 25. The document forgery prevention device according to claim 24, further comprising superimposing means 17, 23, and 24 for superimposing both the light beams. 26 Claim 2, which is provided with an optical path difference forming means 13 that makes the optical path difference between the two light beams variable.
The document forgery prevention device described in Section 5. 27 The document is placed on a swingable holding device, and the determination circuit 20 determines that when the document is rocked, a change in contrast (lμl) of interference fringes appearing on the detection surface 25 exceeds a predetermined value. 26. The document forgery prevention device according to claim 25, which is configured to generate an affirmative signal only when the document is detected. 28. The document forgery prevention device according to claim 24, wherein the signal processing circuit 30 is provided with an electronic correlator. 29 The average scattering angles θ and θ′ of the extracted light beams 10 and 11 are changed using a driving device,
The determination circuits 20 and 31 determine the measured quantity (l
Anti-counterfeiting device according to any one of claims 24 to 28, wherein μl, g ² ) is compared with a stored threshold function. 30. The document forgery prevention device according to claim 24, wherein the document, a light source, and a mirror for reversing both light beams are arranged on a swingable table. 31. The document forgery prevention device according to claim 24, 25, 26, 28, or 29, wherein the wavelength of the light source 73 is variable.